Brush and spring assembly



1956 A. G. POLENSCHAT 3,231,772

BRUSH AND SPRING ASSEMBLY Filed Jan. 14, 1963 FIG.

INVENTOR.

ALBERT G. POLENSCHAT l'i il FIG.3 ZA/ 7% AT ORNEY United States Patent 3,231,772 BRUSH AND SPRING ASEMBLY Albert G. Polenschat, Brookpark, Ohio, assignor to The Reliable Spring and Wire Forms Company, a corporation of Ohio Filed Jan. 14, 1963, Ser. No. 251,242

" 2 Claims. (Cl. 310246) This invention pertains to a spring device, and more particularly to a spring device for biasing a carbon brush in an electric motor.

In the past clock-type springs made of Phosphor bronze have beenused for biasing the carbon brushes in electric motors. When the brush is new and has its maximum length there is a given load applied to the brush by the spring, and it is desirable that as the brush wears down approximately the same load be applied to the brush. However, in the prior art devices, as the brush wore down the load applied by the spring was greatly reduced. In an attempt to maintain the given spring load throughout the life of the brush, the springs were made with many turns in them. Thus each spring had along developed length, which increased the cost of the spring. In spite of the use of expensive Phosphor bronze spring material, and in spite of the great length of spring material, the spring rate (or force applied by the spring) was not as constant as was desired throughout the life of the carbon brush.

An object of the present invention is to provide a less expensive and better spring for electric motor brushes.

A further object of the present invention is to provide a brush spring for electric motors which is made of stainless steel and which is made of much less material than prior art springs.

Still another object of the present invention is to provide a brush spring of the torsion clock-type which does not require a high pre-load, thereby reducing the wear on the carbon brush, especially in the early part of the life of the brush.

Another object of the present invention is to provide a torsion clock-type spring for use with electric motor brushes wherein the load on the brush is constant Within about 1.5 ounces over the life of the carbon brush, and wherein the fatigue life of the spring is greatly increased.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

With reference to the single sheet of drawing FIGURE 1 is an end view of a portion of an electric motor showing four brushes and springs embodying the invention against the commutator.

FIGURE 2 is an end view of one of the spring devices shown in FIGURE 1, and

FIGURE 3 is a side view of the spring device, and

FIG. 4 is a fragmentary perspective view of one brush, brush box and supporting plate assembly.

With reference to the several figures of the drawing the reference character it indicates a mounting ring which is a portion of the electric motor, and reference character 11 indicates generally a commutator device which rotates inside the ring 10. Since the commutator forms no part of this invention it is not shown in detail. Four similar brush devices are shown secured to the mounting ring 10, though the number involved is of no consequence. Each of the brush holders is secured to the ring by two bolts or the like 12, and each brush holder comprises a metal base member 13 to which is spot welded or otherwise affixed a brush holding channel member 14. The channel member 14 has two laterally extending, fiat mounting sections 15 which are afiixed to the base mem- 'ice her 13, and integral with the flat sections 15 is the upstanding channel section 16. The channel section is notched at 17 in a direction away from the commutator 11.

At one end the base member 13 has an integral upwardly turned ear 18 which extends to a height just above the notch 17. A clock spring 19 has one end secured to the car 18, and approximately 1% turns of the spring are around the ear when the spring is in its free, or unstressed condition. In the free or unstressed condition the other or free end of the spring is only about off of its engaged or operating position. Thus the clock spring is wound only about turn and its free end is positioned in the slot 17. Thus when the spring is in its operating position, there are about two full turns of the spring around the ear 18.

A carbon brush 26 is positioned within the channel member 14, with one end thereof held against the commutator 11 and with the spring 19 hearing against its other end and biasing the brush against the commutator.

An important feature of the invention is to have the ear 18 which secures the fixed end of the spring 19 to the base plate 10 offset from the center of the coils of the spring toward the brush 20 as much as possible. Because of the olfset of the ear 18 toward the brush much less spring material is used, compared to prior art holders wherein the ear extended through the center of the spring coils.

As the brush wears down due to the rotation of the commutator the free end of the spring moves toward the commutator, keeping the brush at all times against the commutator. Eventually when the brush is worn out, the free end of the spring comes into contact with the base of the notch 17, and thereafter the spring bias on the brush drops to zero and it is time to put in new brushes.

One of the big factors in the amount of wear on the brush is the spring pressure. It is desirable to have it as low as possible, consistent with adequate brush pressure against the commutator, and to maintain that pressure throughout the wearing of the brush. However, this ideal condition is not obtainable due to the reduction in the spring pressure as the brush wears.

In prior art devices the spring was about 14 /2 inches long, and there were 4% coils in the free position. To get the desired initial spring pressure during assembly the free end of the spring was wound around the centerpositioned ear about one full turn. The variation in the spring load throughout the life of the brush was 5 to 6 ounces. This meant that in order to have proper brush pressure against the commutator when the brush was nearly worn out, it was essential to overload the brush when it was new. In practice, they usually set the spring pressure so that it was correct when the brush was about one half worn down, and thus the overload at the beginning was not so great. However, near the end of the brush life it was under-loaded compared to ideal conditions.

With the spring of the present invention the length of the spring material is only 8% inches and the load range is constant throughout the life of the brush within 1 /2 ounces. This means that with the new spring arrangement the spring load on the brush is nearly ideal, and it changes only slightly throughout the life of the brush. This greatly reduces wear on the brush compared to the prior art brushes which were overloaded, and almost ideal brush-to-commutator contact can be maintained throughout the life of the brush.

The important feature which leads to this almost ideal brush condition is the offset center connection for the fixed end of the spring, and the reduction in the number of turns of the spring. Greatly improved performance and a cost reduction of about 50% over the old spring was realized.

While there have been described What are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein Without departing from the spirit of the invention, and

it is, therefore, aimed in the appended claims to cover all e such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. A spring device for exerting a substantially constant force on a brush for an electric motor comprising, in combination, a mouting device, a brush holder mounted on said mounting device and adapted to hold a brush in position adjacent the commutator of the electric motor, a coiied'cloci -ty-pespring having a free end and a secured end, connecting means securing said secured end to said mounting device, said spring'having its free end against the said brush within said brush holder to urge said brush against said commutator, said connecting means being offset a substantial amountfrom the center of said coil toa brush in said brush holder, a spring of the spirally wound clock-type connected .to said mounting device ad.- jacent said brush holder and having a fixed end near the center of said spiral and having a free end extending from the outside convolution of said spiral and being in engagement with said brush for urging said brush into engagement with said commutator, connecting means securing the fixed endof said spring to said mounting device located at a position Within the innermost convolution of said coiled spring and offset from the centervthere of toward said brush by an amount at least equal to about one half the radius of the outside convolution of said spiral spring.

References Cited by the'Enarniner UN TED ST S 9 TE TS 1,693,322 11/1928 Stanton BIO-+246 2,602,100 7/1952 'McDonald 26.7.,.-,-'1 2,622,700 12/1952 Geyer 26'7;-1 2,630,316 3/1953 F 0s ter 310-239:"X 2,833,027 5/ 1958 'Foster 267:1

F E N PATE IS 97 4,652 3/1961 Germany.

ORlS L. RADER, Primary Examiner.

MILTON O. HIRSHFIELD, Examiner. 

1. A SPRING DEVICE FOR EXERTING A SUBSTANTIALLY CONSTANT FORCE ON A BRUSH FOR AN ELECTRIC MOTOR COMPRISING, IN COMBINATION, A MOUNTING DEVICE, A BRUSH HOLDER MOUNTED ON SAID MOUNTING DEVICE AND ADAPTED TO HOLD A BRUSH IN POSITION ADJACENT THE COMMUTATOR OF THE ELECTRIC MOTOR, A COLIED CLOCK-TYPE SPRING HAVING A FREE END AND A SECURED END, CONNECTING MEANS SECURING SAID SECURED END TO SAID MOUNTING DEVICE, SAID SPRING HAVING ITS FREE END AGAINST THE SAID BRUSH WITHIN SAID BRUSH HOLDER TO URGE SAID BRUSH AGAINST SAID COMMUTATOR, SAID CONNECTING MEANS BEING OFFSET A SUBSTANTIAL AMOUNT FROM THE CENTER OF SAID COIL TOWARD THE FREE END OF SAID SPRING, THE AMOUNT OF SAID OFFSET BEING SUCH AS TO LOCATE SAID CONNECTING MEANS AT LEAST ABOUT HALF WAY BETWEEN THE CENTER OF SAID COILED SPRING AND THE OUTSIDE THEREOF. 